It's a surprisingly good card fighting game, where the cards relay into moves that your Tekken character uses as if you were playing it normally. It seems quite simple at first, but as you play more and get new cards with various effects it becomes a lot more tactical than first thought. Considering it's a free game that uses in–app purchases, it is also extremely generous in giving you coins and credits to buy or upgrade new cards.

They are apparently going to be releasing physical packs of cards which work with the game in the Summer, which also have QR codes and stuff on them that let you do other things. Not sure if you could play the card game with the physical cards though.